5 replies to this topic

[m42364236k]

Dear colleagues

I have question about water treatment system

in our project in water treatment plant we had on gas sweetening ,the function of this gas sweetening was prepare the sweet gas for water system to decrease the h2s of water to 5ppm in the striping column.

But recently contractor propose to use the nitrogen instead of sweet gas to absorb the h2s from water,

I want to know is it applicable to use the nitrogen for absorbing the h2s from water?

Someone has experience or paper or any design practice about this method?

 

Cheers

Michel Mentol

Facility Engineer

[RockDock]

You could use pretty much any striping medium, if wanted. The question becomes, where do you get the N2? It is ordinarily more expensive to produce N2 than to use steam or natural gas. The next question is, what do you do with the H2S and N2? Won't you need fuel gas to flare it? Now, not only do you have SOx, but probably a significant amount of NOx.

 

I've dealt with roughly 100 sour water strippers in the world. Not a single one used N2 for stripping. It just doesn't seem practical, unless you have some very unique circumstances in your plant.

[m42364236k]

You could use pretty much any striping medium, if wanted. The question becomes, where do you get the N2? It is ordinarily more expensive to produce N2 than to use steam or natural gas. The next question is, what do you do with the H2S and N2? Won't you need fuel gas to flare it? Now, not only do you have SOx, but probably a significant amount of NOx.

 

I've dealt with roughly 100 sour water strippers in the world. Not a single one used N2 for stripping. It just doesn't seem practical, unless you have some very unique circumstances in your plant.

 Dear rock thanks for your reply

Actually in the previous design we had gas sweetening package to sweet the gas and we send this sweet gas in striping column,

In striping column water from the top and sweet gas from the bottom had contact and with this method H2S from water removed,

But right know due to some reason we don’t want to use the sweet gas for water H2S treating

Contractor decided to use the nitrogen in the column instead of sweet gas to decrease the H2S of the water to 5 ppm

 

But I want to know that can we use the nitrogen gas to capture the H2S from the water?

Did you see any plant or did you see in any design practice to use it

Also what about the nitrogen with H2S

Does it need any treating or we can send it to flare?

 

Cheers

Michel Mentol

Facility Engineer

[RockDock]

I don't see any problem with using N2 as far as its ability to remove H2S. As I said before, I've never seen N2 used for this purpose. I don't think it would need to be treated before the flare.

 

However, I would want to evaluate a few things:

 

1. Run a study to see how much fuel gas is needed to flare the N2/H2S. Run a ProMax model to see if that amount of gas may be used in the SWS to provide stripping.

 

2. Run a study to see how much fuel gas is currently being used in the flare. Can that gas be rerouted through the SWS? Use the ProMax model to evaluate that and what the increase in fuel gas is as a result.

 

3. Run a study to evaluate the reboiler duty needed with N2 as stripping gas, versus no stripping gas.

 

Remember, SWS do not need addtional stripping gas. They may work perfectly fine with just a reboiler. I would go this route over N2, if possible to avoid increased NOx emissions.

[m42364236k]

I don't see any problem with using N2 as far as its ability to remove H2S. As I said before, I've never seen N2 used for this purpose. I don't think it would need to be treated before the flare.

 

However, I would want to evaluate a few things:

 

1. Run a study to see how much fuel gas is needed to flare the N2/H2S. Run a ProMax model to see if that amount of gas may be used in the SWS to provide stripping.

 

2. Run a study to see how much fuel gas is currently being used in the flare. Can that gas be rerouted through the SWS? Use the ProMax model to evaluate that and what the increase in fuel gas is as a result.

 

3. Run a study to evaluate the reboiler duty needed with N2 as stripping gas, versus no stripping gas.

 

Remember, SWS do not need addtional stripping gas. They may work perfectly fine with just a reboiler. I would go this route over N2, if possible to avoid increased NOx emissions.

  Dear rock

 

As I understand you say N2 can use instead of sweet gas .

 But how nitrogen can remove the H2S from the water?

 

 Also About your first question 

i don’t understand what you mean.

N2/H2S go directly to flare for burning what is the aim of fuel gas?

About you’re second questing could you explain more

You say about the sweep gas of flare?

 

About using the reboiler 

You mean to use the reboiler instead of stripping column?

It means that with reboiler we can remove the H2S from water and no need N2.

 

Thanks a lot 

 

 

Cheers

Michel Mentol

Facility Engineer

[RockDock]

The N2 will enter the vapor phase in the stripper, decreasing the partial pressure of H2S in the vapor phase. In order to remain in equilibrium, the H2S will leave the liquid phase and enter the vapor phase. There is also an ionic element of stripping H2S I will not get into because it is an acid/base interaction that is minor in comparison to the partial pressure.

 

Any flare system has to have a stable flame. The heating value of the gas being flared needs to be monitored and controlled. It is normally controlled by using natural gas. N2 provides virtually no heating value. So, I think you will probably need fuel gas.

 

The reboiler is just used to create steam from the water already available to you in your sour water. You boil the water and send it up the column as your stripping gas. Then you do not need N2, C1 or an external source of steam.